The invention concerns a security document comprising a transparent security element which is arranged in a window or in a transparent region of the security document and which has a transparent structure layer and a diffractive relief structure shaped into a first surface of the structure layer.
The increasing availability and technical maturity of colour copiers and scanners results in copies which in terms of colour quality and resolution can be less and less distinguished from the original. Therefore security documents are protected by what are referred to as OVDs, that is to say optically variable devices which produce different optical effects in dependence on the angle of view and which are difficult to copy. It is however possible to produce the optical effects by imitated OVDs which give the viewer a comparable optical impression.
DE 197 29 918 A1 discloses a security and/or value-bearing document which at different locations has a security feature and a verification element, wherein the verification element is disposed in coincident relationship with the security feature in order to establish the authenticity of the security feature. The verification element is disposed in a window of the security and/or value-bearing document and contains optical elements such as for example lenses, cylindrical lenses or Fresnel lenses which permit verification of the security feature. It can also be provided that the verification and the security element form moire structures or colour changes when disposed in mutually superposed relationship.
DE 100 40 785 A1 describes a security system in which in incident light, outside the carrier plane, a first security element reconstructs a hologram whose encrypted information is rendered readable by a second security element which is moved into the plane of the hologram by folding the security element.
Such solutions suffer from the disadvantage that they are complicated and expensive to manufacture and presuppose skills and knowledge relating to the use of the security elements.
DE101 299 39 A1 describes an optically variable surface pattern with relief structures for producing at least two representations which can be separately perceived by a viewing person and which upon production of a copy by means of a colour copier, are all transferred on to the copy.
DE 101 290 939 A1 describes an optically variable surface pattern with relief structures for producing at least two representations which can be separately perceived by a viewing person and which upon production of a copy by means of a colour copier, are all transferred on to the copy.
WO 03/059643 A1 discloses a diffractive security element with integrated optical waveguide.
DE 102 54 499 A1 discloses a layer arrangement having a structure which produces a lens-like effect and which has an optical-diffraction action.
DE 103 18 157 A1 describes a film and an optical security element. The film has a carrier layer and a replication layer, wherein a diffractive relief structure is introduced into the replication layer for orientation of a liquid crystal material.
EP 0 012 375 A2 describes an identification card comprising a plurality of layers which have security features in the form of grating images and the card core of which has a window into which is fitted a grating image carrier for the grating image.